The present invention relates to a novel organic electroluminescent device and a method of manufacturing the same.
The organic EL (electroluminescent) device is a structural entity comprising an organic light-emitting layer comprised of an organic compound sandwiched between a pair of electrodes. The organic EL, which is expected to find application in flat panel displays and similar devices, has various characteristics such as high-luminance emission, high-speed response, high energy-converting rate, and high color development.
However, when an organic EL device is driven for long periods of time, the device suffers a degradation in light emission characteristics such as a decrease in overall emission luminosity and a loss of uniformity that produces dark spots. For instance, moisture may be adsorbed from the surfaces of component parts of the organic EL device and propagate into the laminate, which consists of a pair of electrodes with a light-emitting substance sandwiched therebetween, via surface defects in the negative electrode. The resulting delamination between the light-emitting substance and the negative electrode blocks the flow of an electric current to cause photoemission-free spots that appear as dark spots.
To eliminate this drawback of dark spots, it is essential to reduce the level of humidity within the organic EL device. One means for reducing humidity in an organic EL is the use of a protective layer containing a desiccant and a sealing layer that are disposed adjacent to the laminate containing the positive electrode, organic light-emitting substance, and negative electrode (Japanese Unexamined Patent Publication H7-169567).
However, the use of such protective layers gives rise to other problems. For instance, the protective layer results in an increased risk leak currents and a cross talk, both of which tend to produce undesired effects on the photoemission characteristics of the device.
Another method that is used to resolve the moisture problem is the use of an organic EL device comprising a gas-tight housing containing a laminate consisting of a pair of electrodes and an organic electroluminescent substance layer sandwiched between the electrodes. A desiccating means is disposed apart from the laminate comprising diphosphorus pentoxide (P2O5) in a hermetically sealed condition (Japanese Unexamined Patent Publication H3-261091).
However, with this technology, the desiccant P2O5 absorbs atmospheric moisture and dissolves to give phosphoric acid which would adversely affect the laminate. Moreover, the method which can be used for sealing the desiccant P2O5 into the housing is limited so that the technology is not suited for commercial-scale production.
A primary object of the present invention is to provide a more expedient and positive desiccating means for use in an organic EL device.
The inventor of the present invention did much research with the above drawbacks of the prior art in mind and found that the above object can be accomplished by fixing a preformed moisture-absorbing body within a gas-tight housing. The present invention has accordingly been developed.
The present invention, therefore, is directed to the following organic EL devices and methods of manufacturing them.
1. An organic EL device comprising 1) a laminate consisting of a pair of electrodes and an organic light-emitting layer sandwiched therebetween, 2) a gas-tight housing accommodating said laminate and shielding off the external atmosphere and 3) a desiccating means disposed apart from said laminate within said airtight housing, characterized in that a preformed moisture-absorbing body as said desiccating means is fixedly secured to at least one part of said gas-tight housing.
2. An organic EL device according to above paragraph 1 wherein said preformed moisture-absorbing body comprises a desiccant and a resin component.
3. An organic EL device according to above paragraph 1 wherein said preformed moisture-absorbing body is an artifact obtained by shaping a mixture of a desiccant and a resin component into a body.
4. An organic EL device according to the above paragraph 2 or 3 wherein the desiccant comprises at least one member selected from the group consisting of alkaline earth metal oxides and sulfate salts.
5. An organic EL device according to the above paragraph 2 or 3 wherein said resin component is at least one kind of gas-permeable resin.
6. A method of manufacturing an organic EL element comprising 1) providing a laminate consisting of a pair of electrodes and an organic light-emitting layer sandwiched therebetween, 2) providing a gas-tight housing accommodating said laminate and shielding off the external atmosphere and 3) disposing a desiccating means apart from said laminate within said gas-tight housing, characterized in that the method includes a step of fixing said preformed moisture-absorbing body as desiccating means to at least one part of said gas-tight housing.
7. A method of manufacturing an organic EL element comprising 1) providing a laminate consisting of a pair of electrodes and an organic light-emitting layer sandwiched therebetween, 2) providing a airtight housing accommodating said laminate and shielding off the external atmosphere and 3) disposing a desiccating means apart from said laminate within said airtight housing, characterized in that the method includes a first step comprising fabricating a preformed moisture-absorbing body comprising a desiccant and a resin component and a second step comprising fixing said preformed moisture-absorbing body as desiccating means to at least one part of said gas-tight housing.
8. A manufacturing method according to the above paragraph 7 wherein said first step comprises providing a mixture consisting of a desiccant and a resin component into the preformed moisture-absorbing body.